<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type"> </head> <body bgcolor="#ffffff" text="#000000"> Hi there, So I am wanting to learn how to modify my firewall-tables script to figure out the current dynamically assigned IP address on fxp1 and also update the firewall-tables if the dhcpd running on fxp1 reassigns a new IP. Here is the script: #!/bin/sh # #firewall-iptables FWVER= 0.76 # # Initial SIMPLE IP Masquerade test for 2.6 / 2.4 kernels # using IPTABLES. # # Once IP Masquerading has been tested, with this simple # ruleset, it is highly recommended to use a stronger # IPTABLES ruleset either given later in this HOWTO or # from another reputable resource. # # # # Log: # 0.76 - Added comments on why the default policy is ACCEPT # 0.75 - Added more kernel modules to the comments section # 0.74 - the ruleset now uses modprobe vs. insmod # 0.73 - REJECT is not a legal policy yet; back to DROP # 0.72 - Changed the default block behavior to REJECT not DROP # 0.71 - Added clarification that PPPoE users need to use # "ppp0" instead of "eth0" for their external interface # 0.70 - Added commented option for IRC nat module # - Added additional use of environment variables # - Added additional formatting # 0.63 - Added support for the IRC IPTABLES module # 0.62 - Fixed a typo on the MASQ enable line that used eth0 # instead of $EXTIF # 0.61 - Changed the firewall to use variables for the internal # and external interfaces. # 0.60 - 0.50 had a mistake where the ruleset had a rule to DROP # all forwarded packets but it didn't have a rule to ACCEPT # any packets to be forwarded either # - Load the ip_nat_ftp and ip_conntrack_ftp modules by default # 0.50 - Initial draft # echo -e "\n\nLoading simple rc.firewall-iptables version $FWVER..\n" # The location of the iptables and kernel module programs # # If your Linux distribution came with a copy of iptables, # most likely all the programs will be located in /sbin. If # you manually compiled iptables, the default location will # be in /usr/local/sbin # # ** Please use the "whereis iptables" command to figure out # ** where your copy is and change the path below to reflect # ** your setup # IPTABLES=/sbin/iptables #IPTABLES=/usr/local/sbin/iptables DEPMOD=/sbin/depmod MODPROBE=/sbin/modprobe #Setting the EXTERNAL and INTERNAL interfaces for the network # # Each IP Masquerade network needs to have at least one # external and one internal network. The external network # is where the natting will occur and the internal network # should preferably be addressed with a RFC1918 private address # scheme. # # For this example, "eth0" is external and "eth1" is internal" # # # NOTE: If this doesnt EXACTLY fit your configuration, you must # change the EXTIF or INTIF variables above. For example: # # If you are a PPPoE or analog modem user: # # EXTIF="ppp0" # # EXTIF="eth1" INTIF="eth0" #INTIF2="eth0" echo " External Interface: $EXTIF" echo " Internal Interface: $INTIF" #echo " Internal Interface: $INTIF2" #EXTIP="your external IP address" EXTIP="<dhcpd_assigned_ip>" echo " External IP: $EXTIP" #====================================================================== #== No editing beyond this line is required for initial MASQ testing == echo -en " loading modules: " # Need to verify that all modules have all required dependencies # echo " - Verifying that all kernel modules are ok" $DEPMOD -a # With the new IPTABLES code, the core MASQ functionality is now either # modular or compiled into the kernel. This HOWTO shows ALL IPTABLES # options as MODULES. If your kernel is compiled correctly, there is # NO need to load the kernel modules manually. # # NOTE: The following items are listed ONLY for informational reasons. # There is no reason to manual load these modules unless your # kernel is either mis-configured or you intentionally disabled # the kernel module autoloader. # # Upon the commands of starting up IP Masq on the server, the # following kernel modules will be automatically loaded: # # NOTE: Only load the IP MASQ modules you need. All current IP MASQ # modules are shown below but are commented out from loading. # =============================================================== echo "----------------------------------------------------------------------" #Load the main body of the IPTABLES module - "iptable" # - Loaded automatically when the "iptables" command is invoked # # - Loaded manually to clean up kernel auto-loading timing issues # echo -en "ip_tables, " $MODPROBE ip_tables #Load the IPTABLES filtering module - "iptable_filter" # - Loaded automatically when filter policies are activated #Load the stateful connection tracking framework - "ip_conntrack" # # The conntrack module in itself does nothing without other specific # conntrack modules being loaded afterwards such as the "ip_conntrack_ftp" # module # # - This module is loaded automatically when MASQ functionality is # enabled # # - Loaded manually to clean up kernel auto-loading timing issues # echo -en "ip_conntrack, " $MODPROBE ip_conntrack #Load the FTP tracking mechanism for full FTP tracking # # Enabled by default -- insert a "#" on the next line to deactivate # echo -en "ip_conntrack_ftp, " $MODPROBE ip_conntrack_ftp #Load the IRC tracking mechanism for full IRC tracking # # Enabled by default -- insert a "#" on the next line to deactivate # echo -en "ip_conntrack_irc, " $MODPROBE ip_conntrack_irc #Load the general IPTABLES NAT code - "iptable_nat" # - Loaded automatically when MASQ functionality is turned on # # - Loaded manually to clean up kernel auto-loading timing issues # echo -en "iptable_nat, " $MODPROBE iptable_nat #Loads the FTP NAT functionality into the core IPTABLES code # Required to support non-PASV FTP. # # Enabled by default -- insert a "#" on the next line to deactivate # echo -en "ip_nat_ftp, " $MODPROBE ip_nat_ftp #Loads the IRC NAT functionality into the core IPTABLES code # Required to support NAT of IRC DCC requests # # Disabled by default -- remove the "#" on the next line to activate # #echo -e "ip_nat_irc" #$MODPROBE ip_nat_irc echo "----------------------------------------------------------------------" # Just to be complete, here is a partial list of some of the other # IPTABLES kernel modules and their function. Please note that most # of these modules (the ipt ones) are automatically loaded by the # master kernel module for proper operation and don't need to be # manually loaded. # -------------------------------------------------------------------- # # ip_nat_snmp_basic - this module allows for proper NATing of some # SNMP traffic # # iptable_mangle - this target allows for packets to be # manipulated for things like the TCPMSS # option, etc. # # -- # # ipt_mark - this target marks a given packet for future action. # This automatically loads the ipt_MARK module # # ipt_tcpmss - this target allows to manipulate the TCP MSS # option for braindead remote firewalls. # This automatically loads the ipt_TCPMSS module # # ipt_limit - this target allows for packets to be limited to # to many hits per sec/min/hr # # ipt_multiport - this match allows for targets within a range # of port numbers vs. listing each port individually # # ipt_state - this match allows to catch packets with various # IP and TCP flags set/unset # # ipt_unclean - this match allows to catch packets that have invalid # IP/TCP flags set # # iptable_filter - this module allows for packets to be DROPped, # REJECTed, or LOGged. This module automatically # loads the following modules: # # ipt_LOG - this target allows for packets to be # logged # # ipt_REJECT - this target DROPs the packet and returns # a configurable ICMP packet back to the # sender. # echo -e " Done loading modules.\n" #CRITICAL: Enable IP forwarding since it is disabled by default since # # Redhat Users: you may try changing the options in # /etc/sysconfig/network from: # # FORWARD_IPV4=false # to # FORWARD_IPV4=true # echo " Enabling forwarding.." echo "1" > /proc/sys/net/ipv4/ip_forward # Dynamic IP users: # # If you get your IP address dynamically from SLIP, PPP, or DHCP, # enable this following option. This enables dynamic-address hacking # which makes the life with Diald and similar programs much easier. # echo " Enabling DynamicAddr.." echo "1" > /proc/sys/net/ipv4/ip_dynaddr # Enable simple IP forwarding and Masquerading # # NOTE: In IPTABLES speak, IP Masquerading is a form of SourceNAT or SNAT. # # NOTE #2: The following is an example for an internal LAN address in the # 192.168.0.x network with a 255.255.255.0 or a "24" bit subnet mask # connecting to the Internet on external interface "eth0". This # example will MASQ internal traffic out to the Internet but not # allow non-initiated traffic into your internal network. # # # ** Please change the above network numbers, subnet mask, and your # *** Internet connection interface name to match your setup # #Clearing any previous configuration # # Unless specified, the defaults for INPUT and OUTPUT is ACCEPT # The default for FORWARD is DROP (REJECT is not a valid policy) # # Isn't ACCEPT insecure? To some degree, YES, but this is our testing # phase. Once we know that IPMASQ is working well, I recommend you run # the rc.firewall-*-stronger rulesets which set the defaults to DROP but # also include the critical additional rulesets to still let you connect to # the IPMASQ server, etc. # echo " Clearing any existing rules and setting default policy.." $IPTABLES -P INPUT ACCEPT $IPTABLES -F INPUT $IPTABLES -P OUTPUT ACCEPT $IPTABLES -F OUTPUT $IPTABLES -P FORWARD DROP $IPTABLES -F FORWARD $IPTABLES -t nat -F echo " FWD: Allow all connections OUT and only existing and related ones IN" $IPTABLES -A FORWARD -i $EXTIF -o $INTIF -m state --state ESTABLISHED,RELATED -j ACCEPT $IPTABLES -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT $IPTABLES -A FORWARD -j LOG #$IPTABLES -A FORWARD -i $EXTIF -o $INTIF2 -m state --state ESTABLISHED,RELATED \-j ACCEPT #$IPTABLES -A FORWARD -i $INTIF -o $INTIF2 -m state --state ESTABLISHED,RELATED \-j ACCEPT #$IPTABLES -A FORWARD -i $INTIF2 -o $INTIF -m state --state ESTABLISHED,RELATED \-j ACCEPT #$IPTABLES -A FORWARD -i $INTIF2 -o $EXTIF -j ACCEPT $IPTABLES -t nat -A POSTROUTING -o $EXTIF -j SNAT --to $EXTIP echo " Enabling SNAT (MASQUERADE) functionality on $EXTIF" $IPTABLES -t nat -A POSTROUTING -o $EXTIF -j MASQUERADE echo -e "\nrc.firewall-iptables v$FWVER done.\n" cheers, Noah </body> </html>